Antimicrobial containment cap for a bone anchored prosthesis mounting

ABSTRACT

An antimicrobial containment cap is provided for use in a bone anchored prosthesis mounting system of the type having an externally protruding fixator pin carried by implanted bone anchored mounting post, wherein the fixator pin accommodates removable attachment to an exoskeletal prosthesis such as a prosthetic limb or the like for an amputee. The containment cap, when mounted onto the fixator pin, is interposed between the prosthesis and soft tissue covering the end or stump of an amputated residual limb or the like. The containment cap carries and supports a selected antimicrobial or antibacterial agent in substantial contact with the soft stump tissue in a position closely overlying and substantially circumscribing the tissue interface with the externally protruding fixator pin to safeguard against infection. The containment cap is adapted for quick and easy periodic removal for cleaning and/or replenishment of the antimicrobial agent.

BACKGROUND OF THE INVENTION

This invention relates generally to improvements in external orexoskeletal prosthetic devices and systems of the type utilizing animplanted, bone anchored mounting post having or carrying an externallyprotruding or externally exposed fixator structure for removableattachment of a prosthesis such as a prosthetic limb or the like. Moreparticularly, this invention relates to an antimicrobial containment capfor use in combination with a bone anchored prosthesis mounting system,wherein the containment cap supports and retains a selectedantimicrobial agent against the skin of an amputee substantially at theexit site or tissue interface of the fixator structure extending throughthe skin, to reduce or eliminate risk of infection.

Socket type prosthetic limbs such as prosthetic arm and leg structuresfor use by amputees are generally well known in the art, wherein aprosthesis is constructed with an open-ended and typically padded socketstructure for receiving and supporting the post-surgical stump of aresidual amputated limb. By way of example, a socket type prosthetic legincludes such open-ended socket structure at an upper end thereof forreceiving and supporting the post-surgical upper leg of a transfemoralamputee. Various straps and/or other fasteners are provided for securingthe prosthetic leg to the amputated limb to accommodate walking mobilityat least on a limited basis. Such prosthetic limbs can be an importantfactor in both physical and mental rehabilitation of an amputee.

However, socket type prosthetic limbs are associated with a number ofrecognized limitations and disadvantages. In particular, the socketstyle prosthesis inherently couples mechanical loads associated withnormal ambulatory activity through a soft tissue interface defined bythe soft tissue covering the end or stump of the residual amputatedlimb, but wherein this soft tissue interface is structurally unsuitedfor this purpose. While many different arrangements and configurationsfor the requisite straps and other fasteners have been proposed forimproved transmission and distribution of these mechanical loads to bonestructures for improved secure and stable prosthesis attachment, tocorrespondingly accommodate a more natural ambulatory movement, sucharrangements have achieved only limited success. In addition,compressive loading of this soft tissue interface often results inblisters, sores, chafing and other undesirable skin irritation problemswhich have been addressed primarily by adding soft padding materialwithin the socket structure. But such soft padding material undesirablyincreases the extent of the soft or non-rigid interface between theamputated limb and prosthesis, all in a manner that is incompatible withan optimally secure and stable prosthesis connection, As a result,particularly in the case of a prosthetic leg, traditional socket styleconnection structures and methods have generally failed to accommodate anormal walking motion.

In recent years, improved external or exoskeletal prosthetic deviceshave been proposed, wherein the external prosthesis is structurallylinked by means of a bone anchored mounting system directly to patientbone. In such devices, a rigid mounting post is surgically implanted andattached securely to patient bone as by means of osseointegration or thelike. This implanted mounting post extends from the bone attachment siteand includes or it attached to a fixator pin or post structure thatprotrudes through the overlying soft tissue at the end of the residualamputated limb. Thus, one end of the fixator pin is externally exposedfor suitable and secure attachment to a prosthetic limb or the like. Insuch bone anchored mounting systems, mechanical loads on the prostheticlimb during ambulation are transmitted by the rigid components includingthe external fixator pin and the implanted mounting post directly topatient bone. As a result, conventional mechanical loading of the softtissue interface is avoided, and substantially improved and/or normalpatient movements are accommodated. In addition, the requirement forcompressive loading of the soft tissue at the end of the amputated limbis significantly reduced, to correspondingly reduce incidence ofblisters and other associated skin irritation problems.

Although use of a bone anchored mounting system offers potentiallydramatic improvements in secure and stable prosthetic limb attachment,and corresponding improvements in amputee lifestyle, the exit site orinterface between the externally protruding fixator pin and the softtissue at the end of the residual limb inherently subjects the amputeeto a significant and on-going risk of infection. That is, the softtissue interface with the externally protruding fixator pin is difficultto seal and protect against entry of microbial infection-producingorganisms. The difficulties in adequately sealing this tissue-pininterface are compounded by the presence of multiple and typicallyrandom and irregular-shaped small skin folds formed in the soft tissueat the end of the residual limb, and thus present in the immediatevicinity of the tissue-pin interface. These small skin foldsunfortunately provide multiple shallow channels or pathways which aredifficult to keep clean, many of which lead directly to the tissue-pininterface. Infection at this tissue-pin interface can produce seriouscomplications including eventual loosening and failure of the boneanchored mounting post.

There exists, therefore, a significant need for improvements in and toexternal or exoskeletal prosthetic devices of the type utilizing a boneanchored mounting system, wherein the risk of infection at the softtissue interface with an externally protruding fixator pin issubstantially reduced and/or eliminated. The antimicrobial containmentcap of the present invention fulfills these needs and provides furtherrelated advantages.

SUMMARY OF THE INVENTION

In accordance with the invention, an antimicrobial containment cap isprovided for use in combination with a bone anchored prosthesis mountingsystem. Such bone anchored mounting system includes an implanted boneanchored mounting post adapted for secure and stable affixation topatient bone, wherein the implanted mounting post carries or isconnected to a fixator pin which protrudes through soft skin tissue andthe like covering the end or stump of a residual amputated limb and isadapted for secure and stable attachment to an external or exoskeletalprosthesis such as a prosthetic limb or the like. The containment cap isinterposed between the external prosthesis and the soft tissue at theend of the residual limb, and carries and retains a selectedantimicrobial agent against the amputee's skin in a position generallyclosely overlying and substantially circumscribing the host tissue exitsite or interface between soft tissue and the fixator pin. Thecontainment cap, which is adapted for quick and easy periodic removalfor cleaning and/or replenishment of the antimicrobial agent, thussafeguards the tissue-pin interface against infection.

In one preferred form, the containment cap comprises a generallycup-shaped structure having an open-ended configuration defining acavity adapted for receiving and supporting the selected antimicrobialagent. In a preferred embodiment, the antimicrobial agent may be carriedby or embedded or impregnated within a disk-shaped member formed from arelatively soft and resilient material such as a fibrous batting orgauze or foam material having a size and shape for seated reception intothe open-ended cap cavity. The containment cap further incorporatesfastener means for removable attachment locked onto the external fixatorpin, such as a central cylindrical hub depending from a cap base wall. Aset screw or the like may be fastened through the depending hub intoengagement with the fixator pin, when the containment cap is slidably orrotatably fitted onto the fixator pin with the soft disk-shaped,agent-carrying member contacting or in close proximity to the softtissue of the residual limb substantially at the tissue-pin interface.The fixator pin protrudes through and beyond the containment cap todefine a free end exposed for suitable removable attachment to theassociated prosthesis, such as a prosthetic leg or arm for an amputee.

In use, the containment cap closely overlies the soft tissue interfacewith the externally protruding fixator pin, to retain the antimicrobialagent against and in close proximity with this soft tissue interfacethroughout normal usage of the prosthesis. The selected antimicrobialagent may comprise any selected medicant in ointment, gel, lotion orother form chosen for killing any selected infection-causing organism ororganisms, or other medicant such as a conditioning or anti-inflammationagent or the like. Upon removal of the prosthesis, the containment capcan be quickly and easily removed from the fixator pin for appropriatecleaning of the residual limb soft tissue and/or cap surfaces, as wellas replenishment and/or replacement of the infection-preventive agent.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconnection with the accompanying drawing which illustrate, by way ofexample, the principals of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is an exploded and partially fragmented perspective view showingthe antimicrobial containment cap of the present invention incombination with a bone anchored prosthesis mounting post for use inremovable external attachment to an exoskeletal prosthesis, such as aprosthetic leg;

FIG. 2 is a fragmented perspective view illustrating an upper legportion of a transfemoral amputee, including a bone anchored prosthesismounting post defining an externally protruding fixator post member foruse in removable attachment of an exoskeletal prosthesis;

FIG. 3 is an enlarged sectional view of the antimicrobial containmentcap of the present invention;

FIG. 4 is an elevation view, shown partially in vertical section,showing the antimicrobrial containment cap mounted onto the externallyprotruding fixator post;

FIG. 5 is an exploded and partially fragmented perspective viewdepicting surgical implantation of the bone anchored mounting post;

FIG. 6 is an enlarged sectional view similar to FIG. 3, but illustratingone alternative preferred form of the invention; and

FIG. 7 is an enlarged sectional view similar to FIGS. 3 and 6, butshowing a further alternative preferred form of the invention.

DETAILED DESCRIPTION

As shown in the exemplary drawings, an antimicrobial containment capreferred to generally in FIG. 1 by the reference numeral 10 is providedfor use with a bone anchored mounting system of the type having animplanted mounting post 12 designed for secure and stable attachment toan external or exoskeletal prosthesis 14, such as a prosthetic limb orthe like for an amputee. The containment cap 10 carries and retains aselected medicant in a position for contacting soft tissue substantiallyat the exit site or tissue interface with an externally protrudingfixator pin or post 16 adapted for removable connection to the externalprosthesis 14. The containment cap 10 is designed for significantlyreducing or eliminating risk of infection at this soft tissue interfacewith the externally protruding fixator pin 16.

The antimicrobial containment cap 10 of the present invention isparticularly designed for use with external or exoskeletal prostheticfixation or mounting systems of the type having the internal, implantedbone anchored mounting post 12 which is surgically attached to andsecurely supported by patient bone, as by means of osseointegration orthe like. For example, with reference to the illustrative drawings asviewed in FIGS. 1-2 and 4-5, the bone anchored mounting post 12comprises an elongated tube or rod formed typically from a high strengthand biocompatible metal or the like adapted for secure affixation withinthe intramedullary canal 18 of a long patient bone 20 such as by seatedimplantation into a lower end of an amputated femur in the case of atransfemoral amputee. The mounting post 12 extends from the amputatedend of the patient bone 20 through the adjacent and associated softtissue 24 which overlies the amputated bone end and defines the stump ofthe residual amputated limb. Importantly, the mounting post 12 extendsfurther, in a one-piece or multi-piece construction, through this softtissue 24 of the residual limb to define the externally protrudingfixator pin 16 for attachment in any suitable manner (not shown herein)to the exoskeletal prosthesis 14, such as a prosthetic leg in the caseof a transfemoral amputee.

The implanted bone anchored mounting post 12 and associated externallyprotruding fixator pin 16 beneficially accommodate direct mechanicalsupport of the prosthesis 14 and associated direct mechanical loading bythe patient bone 20 during normal use such as during ambulatorymovements. In other words, such mechanical loads are transmitted fromthe prosthesis 14 directly via the rigid linkage defined by the fixatorpin 16 and the mounting post 12 to the patient bone 20, whereinambulatory loading is substantially carried by the bone 20 in a normalanatomical manner. By contrast, the soft tissue 24 at the end of theresidual limb is substantially unloaded, compressively or otherwise,since the soft tissue 24 is not required to bear or transmit thesemechanical loads. As a result, the bone anchored mounting systembeneficially provides a more stable and more secure attachment of theprosthesis 14 to the amputee in a manner capable of accommodating morenormal and more natural ambulatory movements. By avoiding significantmechanical loading of the soft tissue 24, soft tissue blistering andchafing and other skin irritation problems associated with a traditionalsoft tissue loaded prosthesis interface are substantially reduced and/oreliminated. In addition, by mechanically linking and supporting theprosthesis 14 from the patient bone 20, amputees have reported asignificant increase in perception of the prosthesis 14 as an actual andnatural body part—a highly desirable factor referred to as“osseoperception.”

The antimicrobial containment cap 10 of the present invention isdesigned for mounting along the externally protruding portion of thefixator pin 16 substantially at the soft tissue interface with saidfixator pin 16, and interposed between the residual limb soft tissue 24and the associated prosthesis 14. Accordingly, in a preferredorientation as shown, the containment cap 10 may be sized and shaped forsubstantially nested positioning within an upwardly open socket 26(FIG. 1) formed in or defined by an upper end of the associatedprosthesis 14, whereby the cap 10 is substantially concealed from viewduring normal use. The containment cap 10 is, in the preferred form,mounted onto the fixator pin 16 but in a manner that does not interferewith the desired direct transfer of mechanical loads by the fixator pin16 and associated mounting post 12 from the prosthesis 14 to the patientbone 20. In other words, the containment cap 10 may be carried by thefixator pin 16 in a manner that does not result in substantialcompressive loads applied to the cap 10 or to the soft tissue 24 of theresidual limb. Importantly, the containment cap 10 supports and retainsthe selected medicant such as an antimicrobial agent in substantialcontact or in close proximity with the soft tissue 24, substantially atthe tissue interface with the protruding fixator pin 16, to reduceand/or eliminate risk of infection.

As shown best in FIGS. 1, 3 and 4, the containment cap 10 comprises (inone preferred form) a substantially cup-shaped body 28 defining anopen-ended or upwardly open cavity 30 including a generally circularbase wall 32 joined at its perimeter with a short, upstanding side wall34 of generally cylindrical shape. A central bore 36 is formed in thebase wall 32 and defines a passage through a short, vertically orientedmounting hub or mounting collar 38 protruding downwardly therefrom. Aradially oriented threaded port 40 is formed in the mounting collar 38for thread-in reception of a fastener such as a set screw 42 or thelike.

In use, the above-described containment cap 10 is mounted onto theexposed end of the fixator pin 16 by slidably fitting the pin 16 throughthe hub bore 36. The cap 10 is adjustably positioned along the length ofthe fixator pin 16 to position and preferably seat an upper margin 44 ofthe side wall 34 firmly but with a relatively light force against thesoft tissue 24 of the residual limb. When suitably positioned, the setscrew 42 or the like can be appropriately advanced within the threadedport 40 to engage the fixator pin 16, thereby locking the containmentcap 10 in place on the fixator pin 16.

Prior to such positional adjustment and positional locking of thecontainment cap 10 onto the fixator pin 16, the selected medicant suchas the selected antimicrobial agent is placed into the cap cavity 30.Accordingly, when the cap 10 is locked onto the fixator pin 16 asdescribed above, the medicant carried thereby is positionedsubstantially against the soft patient 24 located at and surrounding orcircumscribing the soft tissue interface with the fixator pin 16 at theexit site of the pin 16 from the tissue 24 at the end of the residuallimb. Importantly, since this soft tissue 24 typically incorporatesnumerous relatively small or shallow ridges and folds and associatedintervening channels 46 (FIG. 2) extending typically in a generallyradial direction relative to the fixator pin 16, and thus definingtypically hard-to-clean pathways leading to the pin-tissue interface,the presence of the medicant at this location beneficially deters and/oreliminates risk of undesirable infection.

In the preferred form, the antimicrobial agent can be carried by and/orembedded within a soft and resilient member 48 such as a disk-shapedfibrous or gauze or foam pad. Such pad 48 may be formed with a size andshape for slide-fit reception into the cap cavity 30, and may include acentral bore 50 for slide-fit reception over the fixator pin 16 as thecontainment cap 10 is mounted thereon. The pad 48 may have a thicknessfor slight compression against the soft tissue 24 upon final positioningof the cap 10, thereby insuring relatively intimate medicant contactwith the pin-tissue interface.

The selected medicant such as the selected antimicrobial agent may beprovided in any convenient form such as an ointment or gel or salve orthe like, suitable for carrying by the soft pad 48 against the softtissue 24. Various medicants may be used, such as antibacterial orantibiotic compounds and/or combinations thereof suitable for killinginfection-causing organisms at the pin-tissue interface. Alternativemedicants can be used, including but not limited to conditioning oranti-inflammation agents and the like.

Upon periodic and typically normal removal of the prosthesis 14 from thefixator pin 16, the containment cap 10 can be removed quickly and easilyfrom the fixator pin 16 for convenient cleaning and/or replenishment ofthe medicant and/or soft pad 48, or alternately for disposal andreplacement of these components. In this regard, the containment cap 10may be constructed from a metal material suitable for cleaning andre-use, or alternately from a lightweight plastic material or the likeconducive to single usage followed by disposal. The soft pad 48 may alsobe designed for cleaning and re-use with medicant replenishment, oralternately for single usage and disposal. When removed from the fixatorpin 16, the soft tissue 24 is conveniently exposed for cleaning.

FIG. 5 depicts one preferred form for the bone anchored mounting post 12and associated fixator pin 16 with the containment cap 10 for assemblytherewith. As shown, the bone anchored mounting post 12 comprises anelongated and generally tubular component 60 having longitudinallyextending external flutes 62 formed thereon, and a closed upper end 64.Outer surfaces of the post 12 may be constructed to include porous boneingrowth surfaces (not shown) for improved osseointegration, if desired.This mounting post 12 is sized and shaped for suitable surgicalimplantation and secure affixation within the medullary canal 18 of thepatient bone 20, such as an amputated femur. Persons skilled in the art,however, will recognize and appreciate that alternative mounting postconfigurations and affixation techniques, including but not limited tothread-in post structures, may be used.

The fixator pin 16 shown in FIG. 5 includes an upper end 66 having asuitable size and configuration for seated reception and secureaffixation as by press-fitting into the open lower end of the post 12. Aradially enlarged flange 68 may be formed on the pin 16 to provide anenlarged and stable stop for seating against the lower end of theamputated bone 20. The fixator pin 16 protrudes coaxially with theimplanted anchoring post 12 downwardly from the stop flange 68 forpassage through the soft tissue 24 (FIGS. 1, 2 and 4) at the end of theresidual limb, and appropriate removable attachment of the containmentcap 10 and associated prosthesis 14, as previously shown and describedherein. As shown, this externally protruding end of the fixator pin 16may have a noncircular cross sectional shape, such as the squared crosssectional shape as shown in FIG. 5, for suitable secure attachment tothe external prosthesis 14 (not shown).

FIGS. 6 and 7 illustrate alternative preferred forms of the containmentcap 10 of the present invention, wherein components corresponding withthose shown and described in FIGS. 1-5 are identified by commonreference numerals. In this regard, FIG. 6 illustrates one preferredalternative containment cap configuration 110, wherein the disk-shapedand medicant-supporting soft pad 48 is carried by a circular base wall32 in the absence of an upstanding cylindrical side wall 34 of the typeshown and described in FIGS. 1, 3 and 4. FIG. 7 shows anotheralternative preferred containment cap form 210 constructed according toFIGS. 1, 3 and 4 but wherein the upper margin 44 of an upstanding capside wall 34 merges with a radially outwardly extending support flange70 defining a broad-based surface area for contacting the soft tissue 24at the end of the residual limb. In both embodiments of FIGS. 6 and 7,the modified containment caps 110 and 210 are adapted for removablemounting onto the fixator pin 16 in substantially the same manner aspreviously shown and described, to support and retain the soft pad 48and associated antimicrobial agent carded thereby against the pin-tissueinterface.

Although various embodiments and alternatives have been described indetail for purposes of illustration, various further modifications maybe made without departing from the scope and spirit of the invention.For example, although shown and described in connection with a boneanchored mounting post protruding from the patient's body, personsskilled in the art will recognize and appreciate that the containmentcap may be used with other rigid and nonrigid structures protruding fromthe human body. By way of further example, it will be recognized andappreciated that the containment cap may incorporate vented ports asdepicted in dotted lines by reference numeral 80 in FIGS. 3, 6 and 7 toaccommodate air flow to and ventilation of the pin-tissue interface.Accordingly, no limitation on the invention is intended by way of theforegoing description and accompanying drawings, except as set forth inthe appended claims.

What is claimed is:
 1. A containment cap for use in an exoskeletalprosthesis system including a bone anchored mounting post with a fixatorstructure protruding from the mounting post through soft tissue at theend of a residual limb and defining a free end for attachment to aprosthesis, the containment cap comprising: a base defining a perimeter;a side wall integrally formed with the base and extending around theperimeter of the base and defining a cavity configured to receive andsupport a selected medicant in a position closely overlying andsubstantially circumscribing an interface between the soft tissue at theend of the residual limb and the fixator structure; a mounting hubextending from the base; and a bore formed in the base and extendingthrough the mounting hub, the bore configured to receive the fixatorstructure, the bore being the only opening in the base and the side wallconfigured to receive the fixator structure.
 2. The containment cap ofclaim 1, further comprising a radially outwardly extending flangeintegrally formed with the side wall, the flange configured to contactthe soft tissue at the end of the residual limb when the mounting hub isremovably locked to the fixator structure.
 3. The containment cap ofclaim 1, further comprising a resilient member configured to be receivedwithin the cavity, the resilient member configured to receive andsupport the selected medicant.
 4. The containment cap of claim 2,wherein the resilient member is positioned within the cavity and tocontact the soft tissue at the end of the residual limb, the resilientmember having a thickness that provides for at least some compressionwhen the mounting hub is removably locked to the fixator structure.